The use of transoms and bolsters between side frames in railway car trucks is well known. In the main, such transoms have been stiff closed structures, such as tubular members, used to prevent relative movement between the side frames which they connect, thereby providing rigid truck frames.
Some patents disclosing "I" beam or similar type structures in railway car trucks include U.S. Pat. Nos. 792,482; 942,048; 1,962,893; 1,952,819; and 2,908,230. These patents do not include structures designed for slight twisting to permit weaving of side frames in a railway truck.
It is desirable in fixed truck frames to provide equalization. Equalization requirements assure that a wheel of a truck does not lose contact with the rail when the car is traveling over an uneven track, since one wheel leaving the track could cause derailment.